Maneuverability is important with electrically movable vehicles such as wheelchairs. Accordingly, techniques are disclosed as to electrically movable vehicles which realize maneuverability approximate to turning as imaged by the user (see, for example, the publication of JP-A No. 2001-104396, page 1). The electrically movable vehicle disclosed in the patent literature is driven by controlling the operation of a first motor for driving the right wheel and a second motor for driving the left wheel by a controller according to the manipulation of a joystick lever. Stated more specifically, use is made of the angle of inclination of the joystick lever and the direction of inclination of the lever as input data as to the state of the lever as inclined by the manipulator toward the direction of turning. The controller calculates the distance from the current position to a forward target point to be moved past by turning. If the target point is far, the motors are so controlled as to turn the vehicle with a radius greater than when the target point is near. If the target point is near, the motors are so controlled as to move the vehicle to move pat the neighborhood of the current position and the target point.
As disclosed in the above patent literature, it is common practice to control the operation of the left and right wheels individually to turn the vehicle. With the vehicle disclosed in the patent literature, the target values for driving the left and right wheels are defined in terms of distances to be run to reach the target points of the respective wheels. For the vehicle to turn in this case, translating motion is required. In the mode of control disclosed in the patent literature, therefore, it is impossible to turn the vehicle in situ without involving translation.
In the above patent literature, the target value for the drive wheel is finally provided with consideration given to a force (so called lateral G) due to gravity eventually acting on the drive wheel horizontally of the vehicle, spin velocity and limit to the rotational speed of the wheel. In this case, a control value is determined by comparing a value calculated from conditions involving lateral G, spin velocity and limit to the rotational speed of the wheel so as not to exceed these conditions, with a value calculated from the input command value and judging the result of comparison. Accordingly, the control program becomes complex in structure due to increased number of condition judging steps and a specific processing procedure required for the value of the command input unit.
An object of the prevent invention, which has been accomplished in view of the above problem, is to provide an electrically movable vehicle which can be driven by a simplified mode of control and a control program for driving the vehicle.